Modern motor vehicles are typically equipped with heating and ventilation systems for supplying airflow to the vehicle's cabin, i.e. passenger compartment. Heating and ventilation system airflow may be supplied either from ambient or re-circulated air, and may be additionally cooled or heated by the system prior to reaching the passenger compartment.
In most vehicles, engine coolant, usually a mixture of water and anti-freeze, is circulated between an operating internal combustion engine and a radiator, in order to remove excess heat. Some of the hot coolant may be diverted to the heating and ventilation system's heater core, i.e. a radiator-like heat exchanger, to supply heat to the vehicle cabin. The hot coolant is typically supplied to the heater core by an engine-driven pump. The coolant is usually returned to the engine's cooling circuit following the coolant being channeled through the heater core to give off heat. In such systems, the heating and ventilation system typically uses a fan to force air through fins on the heater core and then directs heated air through air vents into the cabin.
There may be situations where there is a need to extend delivery of heat to the cabin even after the engine has been turned off. When the engine is turned off an engine-driven pump also becomes inactive and thus can no longer circulate coolant to the heater core. Without hot engine coolant being circulated cabin airflow returns to ambient temperature fairly rapidly.
Electrically driven auxiliary fluid pumps have been utilized in an effort to prolong delivery of heated air and maintain comfortable vehicle cabin environment after engine shut-down. However, as the vehicle's engine ceases to operate, the temperature of engine coolant begins to drop, thereby steadily losing its effectiveness in heating the cabin airflow. Hence, a heating and ventilation system capable of prolonging delivery of heated air to the vehicle passenger compartment when the vehicle's engine has been turned off would be quite desirable.